This invention relates to the art of tire inflating and deflating systems for vehicles and, more particularly, to a wheel seal assembly for vehicles having an on-board tire inflating and deflating system.
It is of course well known to provide a vehicle with an on-board system and apparatus to enable the vehicle operator to inflate, deflate and/or check the pressure of the vehicle tires with the vehicle at rest or in motion. Such systems and apparatus include a source of air under pressure carried on the vehicle, appropriate valving and controls for the flow of air to and from the tires, and sealing arrangements between fixed parts of the vehicle and rotating parts of the vehicle wheel assemblies which are intended to provide for the delivery of air under pressure to or from the vehicle tires without leakage of air to atmosphere between the sealed surfaces of the fixed and rotating parts.
Sealing assemblies heretofore provided for the foregoing purpose in connection with on-board tire inflating and deflating systems have most often included annular seals of resilient elastomeric material radially interposed between and in constant sealing engagement with the fixed and rotating parts. The seal members are axially spaced apart relative to one another so as to define an annular chamber between the fixed and rotating parts across which air under pressure flows during inflating and deflating operations. Such a seal arrangement is shown in U.S. Pat. No. 4,434,833 to Swanson et al, for example. Among the disadvantages of radial sealing arrangements of the latter character is the fact that the seal members are subjected to constant and uneven wear and thus a relatively rapid deterioration in effectiveness. Uneven wear occurs in part as a result of eccentricity between the fixed and rotating parts, and also results from relative radial or lateral displacement between the fixed and rotating parts during operation of the vehicle. More particularly in this respect, such annular seal members are generally interposed between the fixed axle housing of the vehicle and the rotatable wheel hub portion of the vehicle wheel assembly which is concentric with the axle housing and supported thereon for rotation by bearing assemblies. Accordingly, it will be appreciated that manufacturing tolerances alone preclude obtaining absolutely perfect radial spacing between the fixed and rotating parts engaged by the seal members, thus lending to uneven wear thereof. Additionally, bearing wear in the wheel assembly progressively increases the amount of relative radial or lateral displacement between the fixed and rotating components, thus further promoting uneven wear of the seal components. Moreover, depending on the design of the system, such sealing members are sometimes subjected to constant air pressure from the system, and this promotes wear in general and further promotes and increases uneven seal wear. Yet another disadvantage results from the fact that the elastomeric seal material wears at different rates in connection with different ambient temperature conditions. Such uneven wear leads to leakage across the seal members requiring frequent replacement thereof and the latter results in undesirably high maintenance time requirements and thus down time with respect to use of the vehicle.
In an effort to overcome the foregoing and other disadvantages of such annular radially interposed seals, and to avoid constant wearing interengagement between seals interposed between fixed and rotating parts, I devised a sealing arrangement as shown in my co-pending application Ser. No. 819,716 filed Jan. 17, 1986, now U.S. Pat. No. 4,705,090 and entitled "Method and Apparatus for Controlling Air Pressure in Vehicle Tires" and which is assigned to the same assignee as the present application. That patent discloses a first annular seal member on a fixed vehicle part and which seal member is coaxial with and axially spaced from the vehicle wheel assembly which carries a second seal member rotatable therewith and axially facing the first seal member. The first seal member is normally maintained axially spaced from the second seal member and is axially displaced into engagement with the rotatable second sealing member only during tire inflating and deflating operations. The normally spaced relationship between the seal members minimizes seal wear and, additionally, opening of the sealing area to atmosphere following use of the system provides for the expulsion of air under pressure from the sealing area, whereby the sealing system is effectively self-cleaning.
The sealing arrangement disclosed in my aforementioned patent can serve effectively to reduce sealing component wear by having the sealing components in engagement with one another only during operation of the tire inflating and deflating system. However, such effectiveness requires frequent use of the system, and there is a strong potential for scoring of the sealing surfaces and thus a reduction in the sealing capability thereof and the promotion of wear of the sealing components as a result of long periods of non-use of the system. More particularly in this respect, when such periods of non-use are extensive, although the vehicle is being used, there is a likelihood that dirt and other foreign matter will enter the space between sealing components and thus be captured between the sealing surfaces when the system is next actuated. While opening of the sealing members following operation of the system provides the self-cleaning feature referred to above, such does not effectively avoid contamination of the sealing surfaces in the absence of frequent use of the system. Another disadvantage of my earlier arrangement resides in the fact that moisture can enter the open sealing space, such as during a fording operation of the vehicle, and closing of the seal members and actuation of the system thereafter to inflate the tires operates to blow the moisture into the tires. Furthermore, there is the potential for the displaceable seal member to stick in its normally open position, and/or to bounce axially upon being displaced to engage the second seal member, both of which possibilities are detrimental to efficient operation of the system.